Make LCD reconfigure V3 users when auth data changes

[topnotcher]

CommandGeneratorLcdConfigurator configures auth data and caches based on (username, security engine id). If the authentication data is changed, such as via usmUserAuthKeyChange, the cache is not updated because neither the username nor engine ID changed. Despite new data being passed in, this results in the old data being used and a "Wrong SNMP PDU digest" error indication being returned.

Change the LCD to detect a changed authKey, authProtocol, privKey, or privProtocol and reconfigure the V3 user as appropriate.

[CLAassistant]

All committers have signed the CLA.

[lextm]

Cherry-picked. Close this one.